Background: The beta decays of 3 H and 6 He can play an important role in testing nuclear wave-function calculations and fixing low-energy constants in effective-field theory approaches. However, there exists a large discrepancy between previous measurements of the 6 He half-life.Purpose: Our measurement aims at resolving this long-standing discrepancy in the 6 He half-life and providing a reliable f t-value and Gamow-Teller matrix element for comparison with theoretical ab-initio calculations.Method: We measured the 6 He half-life by counting the beta-decay electrons with two scintillator detectors operating in coincidence.Results: The measured 6 He half-life is 806.89 ± 0.11stat +0.23 −0.19 syst ms corresponding to a relative precision of 3 × 10 −4 . Calculating the statistical rate function we determined the f t-value to be 803.04 +0.26 −0.23 s. Conclusions: Our result resolves the previous discrepancy by providing a higher-precision result with careful analysis of potential systematic uncertainties. The result provides a reliable basis for future precision comparisons with ab-inito calculations.

Studies of 6He beta decay along with tritium can play an important role in testing ab initio nuclear wave-function calculations and may allow for fixing low-energy constants in effective-field theories. Here, we present an improved determination of the 6He half-life to a relative precision of 3×10(-4). Our value of 806.89±0.11(stat)(-0.19syst)(+0.23)  ms resolves a major discrepancy between previous measurements. Calculating the statistical rate function we determined the ft value to be 803.04(-0.23)(+0.26)  s. The extracted Gamow-Teller matrix element agrees within a few percent with ab initio calculations.

The accurate determination of atomic final states following nuclear β decay plays an important role in several experiments. In particular, the charge state distributions of ions following nuclear β decay are important for determinations of the β − ν angular correlation with improved precision. Beyond the hydrogenic cases, the decay of neutral 6 He presents the simplest case. Our measurement aims at providing benchmarks to test theoretical calculations. The kinematics of Li n+ ions produced following the β decay of 6 He within an electric field were measured using 6 He atoms in the metastable (1s2s, 3 S1) and in the (1s2p, 3 P2) states confined by a magneto-optical trap. The electron shake-off probabilities were deduced including their dependence on ion energy. We find significant discrepancies on the fractions of Li ions in the different charge states with respect to a recent calculation.

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We have developed a position response calibration method for a micro-channel plate (MCP) detector with a delay-line anode position readout scheme. Using an in situ calibration mask, an accuracy of 8 µm and a resolution of 85 µm (FWHM) have been achieved for MeV-scale α particles and ions with energies of ∼10 keV.At this level of accuracy, the difference between the MCP position responses to high-energy α particles and low-energy ions is significant. The improved performance of the MCP detector can find applications in many fields of AMO and nuclear physics. In our case, it helps reducing systematic uncertainties in a high-precision nuclear β-decay experiment.